GB2365531A

GB2365531A - Brushless motor with magnetic position sensor

Info

Publication number: GB2365531A
Application number: GB0107413A
Authority: GB
Inventors: Axel Schumacher
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-03-25
Filing date: 2001-03-23
Publication date: 2002-02-20
Anticipated expiration: 2021-03-23
Also published as: GB0107413D0; FR2806853A1; DE10014982A1; GB2365531B; FR2806853B1

Abstract

A switched reluctance machine (brushless motor) is provided with magnetic sensors for determining the angle r between the rotor 20 and stator 10 (see figures 1 and 2). To reduce the effects of the leakage field of the motor, the current I in the energised phase is reduced in a controlled manner 42 before the turn-off angle is reached. At the turn-off angle, the current is reduced to zero in the known manner 43. The reduction 42 in current is only carried out to the extent necessary to allow the magnetic sensor to deliver an adequate position measurement. The current reduction may take place in a region 45 of high inductance when the rotor poles are substantially aligned with the stator poles, or the current reduction may take place about 10{ before the turn-off angle. The magnetic sensors may be magnetoresistive sensors such as GMR or AMR sensors, or Hall effect sensors.

Description

1 2365531 1 Switched reluctance machine having magnetically operating

position sensors

Prior art

The invention proceeds from a switched reluctance machine, in particular in the form of a motor in a motor vehicle having magnetically operating position sensors of the generic kind defined in the preamble of Claim 1.

Magnetoresistive sensors, so-called AMR sensors, are known for the purpose of position detection in brushless motors, that is to say for determining the rotor position of motors. They are also used for angular measurement for other purposes, such as, for example, as a steering angle sensor. For this purpose, the magnetcresistive sensors measure the direction of a magnetic field that is generated, as a rule, by a sensor magnet. In the case of motors whose rotor position is to be measured, said magnet is normally mounted on the end of the shaft. Its magnetic field consequently rotates with the motor. The sensor element itself is mounted axially in front of the end of the shaft and is permanently joined to the motor housing.

In the case where leakage flux from the motor is absent, the rotor position of the motor can consequently be determined directly from the measurement of the magnetic field direction of the sensor magnet.

2 Problems arise, however, because the motor itself in fact also generates a magnetic leakage field. The fields of the motor and the sensor magnet overlap vectorially at the position of the sensor element and therefore result in a faulty measurement of the rotor position. The level of the error depends crucially on the ratio of the magnitude of the two fields to one another.

In the case of switched reluctance motors, the magnetic field generated by the motor depends strongly on the current, but also on the rotor position. The motor field is large, in particular, at high currents and at rotor poles aligned with one another and in the current carrying phase.

The leakage and interference field of the motor is then large. As a result, the error in the rotor position measured by the magnetoresistive sensor can be unacceptably large.

The object of the present invention is to be able to use sensors that determine the position signal magnetically as position sensors despite the problems with leakage fluxes and interference fields that occur in switched reluctance motors.

Advantages of the invention

Claims

The switched reluctance machine according to the invention having the

characterizing features of Claim 1 has the advantage over the known prior art that, despite the occurrence of leakage fields and interference fields in switched reluctance machines, sensors can be used that operate on a magnetic basis.

3 For this purpose, to avoid or reduce the leakage field of the machine in the switched reluctance machine in accordance with the invention, the machine current is basically reduced in principle in each case prior to reaching the turn- off angle and the reduction is carried out under these circumstances only to the extent necessary so that, despite residual leakage or interference fields of the machine, the sensor delivers a position signal that is still adequate.

The measures stipulated in the further claims make possible advantageous developments and improvements of the switched reluctance machine specified in Claim 1.

is According to a particularly advantageous development of the arrangement according to the invention, the current is reduced in the region of high inductance, i.e. with substantially aligned rotor and stator poles.

In a further advantageous refinement, the respective phase current is reduced in the region of about 100 prior to the actual turn-off angle of the respective phase at a turn-off angle in the switched reluctance machine according to the invention that is equipped with six stator and four rotor poles. The reluctance machine according to the invention is advantageously operated with current regulation.

The invention advantageously makes it possible that magnetoresistive sensors are provided for use as sensors. In an advantageous development, both anisotropic so-called AMR sensors and giant magnetoresistive sensors, so-called GMR sensors are provided as such. In an alternative 4 advantageous refinement, it is also possible in addition that Hall sensors are provided as sensors.

Drawing The invention is described in greater detail in the description below by reference to exemplary embodiments shown in the drawing. In the drawing:

Figure 1 diagrammatically shows a plan view of rotor poles and poles of the energized stator phase in the nonaligned position; Figure 2 diagrammatically shows a plan view of rotor poles is and poles of the energized phase 1 of the stator in an aligned arrangement; Figure 3 shows a diagram of the normalized flux linkage T/T"w, as a function of the normalized phase current I/I,,,, the flux linkage being shown for various rotor positions in a family of curves, and Figure 4 shows a diagram with the normalized current I/I.m,.

plotted against the rotor angle 0 to show the reduction in current in the region of high inductance in the case of aligned stator and rotor poles in accordance with the present invention.

Description of the exemplary embodiment Figure 1 diagrammatically shows a plan view of a stator 10 and a rotor 20 of a switched reluctance machine in the form of a motor, which machine is equipped with six stator and four rotor poles. The stator 10 comprises three pole pairs 1-1, 2-2 and 3-3. The rotor 20 comprises four poles A-A and B-B. The poles 1 of the pole pair 1- 1 are each surrounded by a winding 11. All the poles project inwards towards the rotor from a stator ring. The windings of the pole pairs 2-2 and 3-3 are not shown. In the view of Figure 1, the rotor poles A-A are not aligned opposite the energized winding 11 having the stator poles 1-1. On the contrary, the unaligned rotor angle 0 of 45' is reached here. Figure 1 therefore shows that the rotor poles A-A and the poles 1-1 of the energized phase 1 are not aligned with the winding 11, but that there is a rotor angle of 0 = 450 between them.

Figure 2 shows the same diagrammatic plan view of the stator 10 and the rotor 20 of the switched reluctance machine shown in Figure 1. The two poles 1-1 are again surrounded by the winding 11 and the pole A-A of the rotor 20 are now aligned with the poles 1-1 of the energized phase 1 so that the rotor angle 0 between the poles A and 1 has the value 00. Consequently, in accordance with this view, the rotor poles A-A are mutually aligned with the poles 1-1 of the energized phase 1 according to the energized winding 11 and the rotor angle 0 is o'.

In a family of curves in accordance with Figure 3, the various flux linkages are shown as a function of the 6 normalized phase current, the rotor position having the various angular values acting as parameter. Said family of curves applies to rotor positions in a motor having six stator and four rotor poles. In accordance with the arrow 30, the rotor angle 0 increases from the value 0' to the value 450. In the view in Figure 3, the flux linkage in a normalized representation T/Tmax is plotted against the normalized phase current I/I,a,. The individual values of the rotor angle 0 are marked against the various curves of the family of curves. In this diagram, the poles are aligned at 0' and are unaligned at 45'.

Figure 4 shows a diagram of the phase current and of the reduction in current in accordance with the invention. In this diagram the normalized phase current I/I,,, is shown plotted against the rotor angle 0, which is specified in degrees. With a turn-on angle Of 0on Of 0', the current starts to rise along an edge 40 to the maximum value. Over a serrated region 41, which originates from the timing of the current, the current remains substantially constant at the maximum value. Along a falling curve 42, the current is reduced in the manner according to the invention, between the angle 0 = 31' and 0 = 40' as in the example shown. Under these circumstances, the current variation follows the curve 42. The reduction in current itself takes place within a region 45 that is indicated by the double arrow and that can cover a region of about 1C. Said region 45 is situated in front of the actual turn-off angle 0,,ff of the current energization of the phase. The current energization of the phase is indicated by the double arrow 44 and is situated between the angle 0... and 0,,ff, in the example shown 7 between the value 00 and 400. From the turn-off angle 0,,ff up to the unaligned position of 45', the current decreases along the curve 43 to the value 0. According to the invention, therefore, in the region 44 of the current energization of the respective phase, a region 45 is turned on that is situated in front of the turn-off angle 0,,ff of the respective phase. In said region 45 starting at the reduction angle 0,ed, the current is reduced by a particular and suitable value. In the example shown, the current is reduced to half the maximum value before it is then turned off completely at 0,,ff and falls to the value 0 along the curve 43. Advantageously, the switched reluctance motor is operated with current regulation.

The size of the region 45 for the reduction,in current that takes place before the turn-off angle 0Off of the phase depends on whether, despite the existing interference or leakage field of the switched reluctance machine used as motor, the sensor used still delivers a position signal that allows the position to be unambiguously detected. The setting can be determined, on the one hand, by the size of the reduction in current and, on the other hand, by the angle Ored, i.e. how large the distance from the turn-off angle 0,,ff is.

The reduction in current according to the invention takes place in the region of high inductance, that is to say with stator poles 1-1, 2-2, 3-3 and rotor poles A-A and B-9 aligned. The reduction in current and point in time or angular position of the reduction can be chosen according to the signals needed. During the current reduction itself, the so-called hard or soft type of timing can be used. In 8 the case of hard timing, both transistors in a phase are alternately turned on and off to produce a desired current shape. In the case of soft timing, only one of the two switching transistors is switched per phase. 5 Said reduction in current provided in accordance with the invention in the triggering circuit of the switched reluctance motor makes it possible, despite magnetic interference fields originating from the motor, to use sensors that are based on a magnetic mode of operation. Magnetoresistive sensors, so-called anisotropic magnetoresistive sensors, which are known as AMR sensors, and giant magnetoresistive sensors, which are known as GMR sensors, act as such sensors. Alternatively and in addition thereto, Hall sensors can also be used. In the case of magnetoresistive sensors, the direction of the magnetic field is determined, whereas in the case of Hall sensors, the presence of a magnetic field perpendicular to the conductor of the Hall sensor is detected. In both cases, the position of the rotor with respect to the stator can be determined therefrom. Said position is of crucial importance for the control of the switching times of the current supply or current turnoff to the individual phases in the switched reluctance motor. The sensors are not shown in the figures.

Consequently, the invention advantageously makes it possible in a simple manner without large changes to the method of controlling the motor for magnetoresistive sensors or Hall sensors to be applicable to position detection in switched reluctance motors. The invention suppresses or at least adequately reduces the adverse 9 effect of the leakage field of the motor on the sensor element.

Claims 1. Switched reluctance machine, in particular in the form of a motor in a motor vehicle, having sensors for determining the angle between the rotor (20) and the stator (10) of the machine, wherein the sensors determine the position signal on the basis of a magnetic mode of operation, characterized in that, to avoid or reduce the leakage field of the machine, the machine current is reduced in a controlled manner in each case before the turn-off angle (0,,ff) is reached and wherein the reduction is carried out only to the extent necessary so that, despite residual leakage or interference fields in the machine, the sensor delivers a position signal that is still adequate.
2. Switched reluctance machine according to Claim 1, characterized in that the reduction in current takes.

place in the region of high inductance, i.e. with rotor poles (1-1, 2-2, 3-3) and stator poles (A-A, P-2) substantially aligned.
3. Switched reluctance machine according to Claim 1 or 2, characterized in that, in the case of a reluctance machine that is equipped with six stator poles and four rotor poles, the respective phase current is reduced in the region (45) of about 10' before the actual turn-off angle of the respective phase at the reduction angle (Or,,j).
4. Switched reluctance machine according to one o f Clams 1 to 3, characterized in that the machine is operated with current regulation.
5. Switched reluctance machine according to Claim 1 or one of Claims 2 to 4, characterized in that magnetoresistive sensors are provided as sensors.
6. Switched reluctance machine according to Claim 5, characterized in that anisotropic sensors, so-called AMR sensors, or giant magnetoresistive sensors, so called GMR sensors, are provided as magnetoresistive sensors.
7. Switched reluctance machine according to Claim 1 or one of Claims 2 to 4, characterized in that Hall sensors are provided as sensors.
8. Switched reluctance machine substantially as hereinbefore described with reference to the accompanying drawings.